I was taught if you have a manual, use it.
That, in all honesty, is the best advice you'll find anywhere.
If a manual isn't available, or is out of date like my 10EE manual from Monarch regarding lubrication, consult with people who can provide a citation, reference or strong relative experience. A technical representative, or an actual tribologist.
I'm going to take the "strong relative experience" category. I keep up the mechanical things for a diverse company, ranging from earthmoving stuff, to landscaping and hardscaping equipment, to a fleet of tow trucks. And lord knows how many "incidental" things that probably don't have any proper category. When I took over this position, things were in a bad way.... These days we've got 14 small tow trucks, 5 class 7 ones, on a ten year replacement, ranging from nearly new to theoretically ten years old. A couple survived the rust longer, I think 14 years is our oldest. Last tally was just under seven and a quarter million miles. Some of the loaders are over 30,000 hours. It used to be a big deal when they hit five or six... Of course that's not all about the oil, but obviously that's the big ticket repairs. Pumps, drive motors, engines, transmissions, and so forth. Component failures so expensive that they'll take an otherwise very serviceable unit out of sersomething "llight duty" such asvice, with no residual value besides the scrap steel. I learned early on that the advertising department (from any company, even the good ones) doesn't give a rat's tail about my equipment. As the internet got big, it took about zero time to figure out that the internet doesn't WANT to understand oil. The internet wants a one word answer to oil, and there is not. My experience, and what I write comes from countless hours on the phone with the technical folks from varioius oil distributors over the years, as well as the manufacturers who offer that to smaller accounts. We're big in my world, but microscopic in the corporate world. Not every oil company offers that to just anyone, even "small" customers like we are. So my citations are quite weak in that they are absolutely 99 percent "hearsay" I guess, but while it's not all by phone any more, some stuff does come over the internet, the sources are not "the internet at large".
Looking forward to reading your citations
When I asked about the cross reference between the DTE light and Chevron GST 32, I was leading up to a case in point. These are very comparable, top tier products in a heap of different applications, but the GST, according to Chevron, clearly says that theirs is not for gears. They want you in their AW category for that. You can google yourself there by using "Chevron GST", that gets you the least scrolling to get to a Chevron site instead of a reseller/distributor, who are collectively very prone to shortening or generalizing the original statements.
What does "not for gears" mean to all those folks who have used the very commonly noted similarity and interchange between GST and the Mobil, which as I said, is a benchmark, but is not typically so conveniently available outside of industry? Obviously something, but probably not that much low horsepower application. Possibly not a tangible difference in a lifetime (probably VERY dpendant on any given lathe saddle in this case). But as horsepower through the gears in question rise, at some point in the power transmission scale that issue will be front and center...
Why did I jump on that point so quick? Because this is a rare case where you can skip the internet, and literally just go to the products page, and find a (nearly) accurate, one word answer for the difference, straight from the source. They have a very different approach to boundary and elastohydrodynamic protections in high stress/high pressure applications. That leads to a very unintuitive and backwards conclusion. The heavier duty, more capable oil, (the GST) in a very non intuitive way, offers far, far less protection in the case of the machines we are dealing with.
Go to the source.
Don't trust interchanges to pick a product, use them to hasten the process of doing your own comparison.
Never trust the internet at large. Even if they sound like they're on top of things. That includes me.
